this is a great media player and it is free but it did take a bit to find how to do this and the latest version 3.0.10 in April 2020 seems to have a bug that keeps repeating the video conversion and you need to use Task Manager to shut it down
first you need to go to Tools: Effects and Filters : Video Effects: Geometry and then tick Transform and ensure it's option is “Rotate by 90 degrees”
now when you play your video it will play within VLC in the desired vertical orientation, but if you then save your video by using the Media: Convert/Save these settings will NOT be applied to your converted video!
you need to do one more convoluted, hidden step to ensure your transform is applied to your conversion:
go to Tools:Preferences:Interface Settings page
at bottom left tick All to display the Advanced Settings
open up the tree item Sout stream and then click on Transcode
then tick the “Video Transformation Filter” and hit Save
NOW, you can go to Media: Convert/Save and you will get your vertically oriented video in 9:16 as desired